1. Field of the Invention
The present invention relates to an image formation apparatus, and in particular to a configuration for preventing toner remaining on a photosensitive drum from being given out after a toner image is transferred.
2. Description of the Related Art
Conventionally, in an image formation apparatus such as a copy machine, printer and facsimile which provide image formation by using electrophotographic technology, and after a toner image is formed on a photosensitive drum, i.e. an image bearing member, this toner image is transferred onto a sheet or intermediate transfer belt at a transfer portion. Moreover, when the toner image on the photosensitive drum is transferred at the transfer portion in such a manner, toner may remain on the photosensitive drum, and in such a case, the residual toner may be reclaimed by a cleaning device.
The residual toner may be corrected, for example by bringing a cleaning blade into abutment on the photosensitive drum. However, in the case of using this cleaning blade, because the residual toner may run away transversely on the cleaning blade, a seal 71 is provided on each of ends of a cleaning blade 28 in order to block the toner, as shown in FIG. 6.
Further, on the outside of the seal 71 is disposed a seal 74 for sealing an aperture of a cleaning container, and these two seals 71 and 74, both are arranged to contact with the surface of the photosensitive drum in the entireties of their longitudinal portions.
Moreover, this seal 74 is disposed to always contact with a circumferential abutting surface 82 shown by a shaded area where a spacing member 81 abuts on a photosensitive drum 1, as shown in FIG. 7. Further, this spacing member 81 spaces apart a developing sleeve 4b for supplying toner to the photosensitive drum 1 and the photosensitive drum 1.
Further, this seal 74 is, as disclosed in Japanese Patent Application Laid-Open No. 2000-132027 (see FIG. 8), a two-layer structure composed of a raising member 74a abutting on the photosensitive drum 1 and an elastic member 74b such as a sponge, and the elastic member 74b is attached to a cleaning container 91 by using double-faced adhesive tape.
Then, by providing such a seal 74, even if toner adheres to the spacing member 81 and subsequently to the circumferential abutting surface 82 of the photosensitive drum 1, the residual toner may be wiped off by the seal 74 when the photosensitive drum 1 rotates.
In such a conventional image formation apparatus, an image region has extended more in the direction perpendicular to the sheet feed direction because of demands for paper extension, a frameless image and the like, and therefore, a photosensitive drum tends to extend in width direction.
However, if a photosensitive drum changes in length as such, a conventional drum manufacturing facility becomes unusable so that a new facility is to be necessary, and accordingly, the drum will be expensive. As a result, the entire product cost of an image formation apparatus and service parts costs of a process cartridge and the like will be raised.
Then, to use a photosensitive drum having a conventional length, for example, a cylinder 1a of a photosensitive drum 1 shown in FIG. 9A remains the same, while a flange 1b made of resin may be configured to be wider to provide a longer virtual drum length, as shown in FIG. 9B.
Here, when the drum length is virtually elongated in such a manner, positions of seals 74 shown in FIG. 9A are required to be displaced to positions shown in FIG. 9B. Then, when the seals 74 are moved to the positions shown in FIG. 9B, the seals 74 may be arranged to overlie both the cylinder 1a and the flange 1b. 
However, if the seals 74 are arranged in such configuration, the flanges 1b made of resin may be ground to wear away due to difference between materials of the cylinder 1a and the flanges 1b and difference in surface characteristics. Moreover, if a contact pressure of the seals 74 is configured to be lower so that the flanges 1b may not be ground, seal characteristic cannot be satisfied. That is, if the seals 74 are arranged to overlie both the cylinder 1a and the flanges 1b, it may be difficult to satisfy both endurance and seal characteristic.